CZ300611B6 - Extruder for processing rubber mixtures and method for processing rubber mixtures - Google Patents

Abstract

The present invention relates to an extruder for the preparation of rubber mixtures wherein the extruder is characterized in that the screw (2) is so defined by a helix angle (phi) and a thread depth (H) as to have an entry zone (7) in which the rubber mixture is exposed to an increased pressure (p), and an exit zone (8) in which the rubber mixture is exposed to a constant or decreasing pressure (p), so that the rubber mixture is subjected to a temperature rise during its advance to the extrusion tool (5) as a consequence of heat dissipation to thereby realize an extrudate at a temperature which approximates a vulcanizing temperature for the extrudate. The invention also relates to a method for processing a rubber mixture in the above-described screw extruder, said method comprising the steps of: feeding the rubber mixture to an extruder for plasticizing and shaping into a desired extrudate for subsequent exposure to a vulcanizing process, wherein the rubber mixture is advanced in the extruder by a screw (2) from a screw entry zone (7) under increasing pressure in a direction of a screw exit zone (8) in which the rubber mixture is advanced at a constant or decreasing pressure, wherein a helix angle (phi) and a depth of thread (H) of the screw (2) are selected in such a way that a cylinder (1) exit zone (8) is overshot by a cylinder (1) entry zone (7) to continuously increase the temperature of the rubber mixture; so that the extrudate exits the extruder at a temperature which approximates a vulcanizing temperature of the extrudate.

Description

Extruder for treatment of rubber mixtures and method of treatment of rubber mixtures

Technical field

BACKGROUND OF THE INVENTION The present invention relates to an extruder for treating rubber compositions for elastomeric articles, in particular continuously manufactured elastomeric profiles, with a cylinder, with a screw rotatably mounted therein to draw, convey and homogenize the rubber composition and an injection head with an embossing tool. The invention also relates to a process for treating rubber compositions in a screw extruder in the preparation of the manufacture of elastomeric articles, in particular elastomeric profiles, in which the rubber composition is fed to the extruder, plasticized therein and brought into a mold intended for use. by heat supply, the extrudate undergoes a vulcanization process.

BACKGROUND OF THE INVENTION

In the manufacture of elastomeric articles, a largely uniform degree of crosslinking during the vulcanization process is sought to ensure quality. The difference between the temperature of the extrudate and the temperature of the vulcanizing medium should not be too great. In practice, the extrudate leaving the extruder is brought from 70 to 100 ° C to a high level of initial temperature at the beginning of vulcanization of about 130 to 180 ° C.

For this, a shear-head method can be used in which the mechanical energy of the rotating shear darkness is used to increase the temperature of the extrudate.

Furthermore, there is the possibility of using UK V (ultra-short wave) technology, which, however, requires costly recipe formation especially for mixtures based on nonpolar EPDM polymers.

Further, the prior art, EP 798 097, discloses an extruder having a throttle valve which is driven by a feedback control, based on the measured extrudate starting temperature, from the initial extrudate density and from the extrudate starting weight. This throttle comprises individual, radially outwardly extending barrel walls of the extruder barrel, which are driven by an outwardly driving drive carrier. By varying the length of engagement of these mandrels into the interior of the extruder, the resistance to shearing acting on the conveyed extrudate can be continuously adjusted. The desired extrudate temperature can thus be set depending on the operating parameters. This is a very expensive construction, which must have both a special extruder barrel with which the throttling darkness can be captured from outside and a specially made worm.

This apparatus serves to maintain the desired, optimum temperature of the extrudate, but it is furthermore not said whether the vulcanization temperature should be reached.

Apparatuses are also known in which, in connection to an extruder with an extruder screw, the shear head is rigidly rotatably coupled to the screw, while the surrounding housing and the sleeve connecting the extruder are rotatable opposite to the direction of rotation of the screw. The shear forces acting on the extrudate and hence its temperature can be influenced by the continuously adjustable speed of rotation of the sleeve. This is used in US 4,365,946 to raise the temperature of the rubber composition to the vulcanization temperature.

The disadvantage of the two apparatuses described above lies in the complex construction as well as in the fact that the elements for raising the temperature of the extrudate are toothed with the extruder, which implies that existing extruders cannot be remodeled.

- 1 GB 300611 B6

SUMMARY OF THE INVENTION

It is an object of the invention to provide a uniform cross-linking of the rubber profile of its temperature to a level of approximately vulcanization.

According to the invention, this is achieved in an extruder of the kind mentioned at the beginning in that the pitch angle and the worm depth are mutually selected to create an inlet region of the pressure increasing cylinder in the rubber mixture and an outlet region of the cylinder with constant or decreasing pressure. the mixture on its way to the discharge tool by dissipating heat to bring the extrudate temperature closer to the vulcanization temperature.

The invention is associated with the advantage that complicated devices, such as shearing heads or UK devices, can be dispensed with in the device for raising the temperature after the extruder has exited.

According to an advantageous embodiment of the invention, the screw of the extruder is constructed according to its diameter in a multi-pass, the number of runs increasing as the screw diameter increases. Preferably, the pitch angle and the pitch depth of the screw are selected such that in the extruder, the inlet region with increasing pressure is followed by an outlet region with a constant pressure or pressure drop.

In this case, the screw of the extruder can be designed as a worm of reduced power with a small lead angle in the outlet region, preferably in the range of about 7 to 14 °.

As an alternative to, or in combination with, a small pitch angle, it is possible to provide the extruder screw exit region with a low running depth. Thus, it has proven expedient to select a running depth <0.15 x screw diameter.

In order to set the temperatures of the roll, especially the exit region of the extruder, to the level required by the method of the process without affecting the inlet region, the roll of the extruder may consist of a plurality of structural units which are thermally separated from each other by insulating rings.

In a further embodiment of the invention, a pressure part is inserted into the injection head of the extruder to reduce the free volume and / or increase the pressure in order to adjust the mixing temperature of the rubber mixture by adjusting or adjusting it. by increasing the pressure, both in the screw channel and in the injection head, the pressure energy further increased and the mean residence time at elevated mixing temperatures decreased.

Further, the problem is solved by a method of treatment of rubber mixtures in a screw extruder in the preparation of production of elastomeric products, in particular elastomeric profiles, in which the rubber mixture is fed to the extruder, plasticized therein and brought into the shape intended for use. According to the invention, the rubber mixture is conveyed from the inlet region of the screw under increasing pressure of the rubber mixture in the direction of the outlet region of the screw, which runs at a constant and / or decreasing pressure, the outlet region of the roll passing from the inlet region of the roller. by suitable selection of the running angle and running depth and the rubber mixture is substantially continuously heated by dissipating heat to approach the extrudate temperature after leaving the extruder to the vulcanization temperature.

According to an advantageous embodiment, a screw is used to raise the temperature of the extrudate to a level close to the vulcanization temperature, the geometry of which is dimensioned such that the temperature increase in the baffle mixture of the puff mixture is caused by heat dissipation.

Advantageously, the heat dissipation in the rubber mixture is achieved by increasing the screw speed at a relatively low throughput.

-2GB 300611 B6

BRIEF DESCRIPTION OF THE DRAWINGS

DETAILED DESCRIPTION OF THE DRAWINGS FIG. 1 shows a screw extruder according to the invention, FIG. 2 shows the characteristics of such a screw, and FIG. 3 shows a graphical representation of the mixing temperatures achievable in the stationary operating state of the extruder.

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DETAILED DESCRIPTION OF THE INVENTION

The extruder shown in FIG. 1 consists essentially of a cylinder 1, a screw 2 rotatably provided in the cylinder 1, and an injection head 3 with an inserted pressure part 4 and an extrusion tool 5.

The cylinder 1 is divided by an insulating ring 6 into the inlet area 7 of the cylinder 1 and the outlet area 8 of the cylinder 1, which have cavities 9 and 10 for tempering the cylinder 1.

The screw 2 consists of an inlet region H of the screw 2 and an outlet region 12 of the screw 2, which differ from one another in the pitch angle θ S and in the depth H. Thus, the outlet region 12 of the screw 2 has a smaller running angle> from 7 to 14 ° and a smaller running depth H relative to the entrance area 11 of the screw 2.

The injection head 3, which is shaped in a flow-friendly manner, allows, in conjunction with the inserted pusher 25, parts 4 to be adapted, respectively. increasing the pressure in both the screw channel 2 and the injection head 3 by converting the pressure energy and reducing the mean residence time of the mixture in the extruder at elevated mixing temperatures.

In the operation of the extruder, the rubber mixture is conveyed from the inlet region 11 of the screw 2 in the direction of the outlet region 12 of the screw 2, and by selecting according to the invention there is a reduction in the pressure flow and stray flow, thereby improving the thermal conduction of the process.

Furthermore, due to the increase in the surface / volume ratio resulting from the invention, the mixing temperature in the slowly flowing regions of the walls can be controlled relatively accurately in the outlet region 12 of the screw 2.

For example, the worm 2 having the above effects has the following dimensions:

-3GB 300611 B6

worm parameter / area dimension entry area output area diameter D mm 60 60 length L mm 420 300 running depth H mm 8 5 channel width mm 15.4 18.6 climb S running mm 40.0 47.0 pitch angle φ 0 12 14 width So of bridge mm 4 4 number of courses - 2 2 Surface cm ³ 2 230 1 379 obj em cm ^ 498 231 surface / volume cm ” ¹ 4,5 6.0 t (Q = 50 l / h) min 0.60 0.28

In Fig. 2, the characteristic of such a screw 2 is shown as the conveying flow Q through the pressure p. The EPDM-based mixture was used as the rubber mixture. The various characteristics relate, as can be seen from FIG. 2, to a different number of n turns of the screw 2. The crosslinking behavior of the rubber mixture should be adjusted such that a 10% crosslinking at 140 ° C is achieved after more than 3 minutes.

The temperature of the material obtainable during the operation of the screw extruder 2 according to the invention is shown in FIG. 3 as a function of the number n of the screw 2 at different pressures p and temperatures T10 for the EPDM-based mixture.

Claims (10)

15 PATENT CLAIMS 1. Extruder for the treatment of rubber mixtures for elastomeric products, in particular continuously made elastomeric profiles, with a cylinder (1), with a screw (2) rotatably mounted in a cylinder (1) for inserting, transporting and homogenizing with an embossing tool (5), characterized in that the pitch angle (φ) of the travel (S) and the travel depth (H) of the screw (2) are selected from one another to form the inlet region (7) of the cylinder by the pressure (p) in the rubber mixture, and the outlet region (8) of the cylinder (1) with a constant or decreasing pressure (p) to provide an increase in the temperature of the rubber mixture on its way to the extruder (5) 25 by dissipating heat to bring the extrudate temperature closer to the vulcanization temperature. Extruder according to claim 1, characterized in that the worm (2) is, depending on its diameter (D), formed of a multi-pass, wherein the number of runs is increased as the diameter (d) of the worm (2) increases . 30 An extruder according to claim 1 or 2, characterized in that the screw (2) is provided by a small angle (φ) of the running pitch (S) in the outlet region (12) of the screw (2) with a lowered angle. performance. Extruder according to claim 3, characterized in that the angle (φ) of the pitch (S) of travel at The outlet region (12) of the screw (2) is in the range of 7 to 14 °. -4 CZ 300611 B6 An extruder according to claims 1 to 4, characterized in that the outlet region (12) of the screw (2) has a low running depth (H). 5 Extruder according to claim 5, characterized in that the running depth (H) is less than 0.15 x diameter (D) of screw (2). Extruder according to one of Claims 1 to 6, characterized in that the roller (1) consists of at least two structural units which are separated from one another by thermal insulating rings (6). Extruder according to one of Claims 1 to 7, characterized in that a pressure part (4) is inserted in the injection head (3) to reduce the free volume and / or increase the pressure (p). 15 Dec Method for treating rubber mixtures in a screw extruder in the preparation of the production of elastomeric products, in particular elastomeric profiles, in which the rubber mixture is fed to the extruder, in which the casing is flaked and brought into a shape intended for use in the extruder (5). and then subjecting the extrudate to a vulcanization process by supplying heat, wherein the rubber mixture is conveyed from the inlet region (11) of the screw (2) below the rising 20 by the pressure (p) of the rubber mixture in the direction of the outlet region (12) of the screw (2), which runs at a constant and / or decreasing pressure (p), the outlet region (8) of the roller (1) passing from the inlet region (7) The roller mixture (1) is suitably selected by the pitch angle (φ) and the running depth (H) and the rubber mixture is continuously heated by dissipating heat to approach the extrudate temperature after leaving the extruder to the vulcanization temperature. Method according to claim 9, characterized in that the temperature increase of the rubber mixture is achieved by an increased number (n) of the screw speed (2) at a relatively low throughput.